JP2003046110A - Semiconductor photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor photodetector by which response deceleration is prevented by reducing dark current. SOLUTION: The semiconductor photodetector is obtained by forming a buffer layer 11 presenting a one conductivity type, a semiconductor layer 12 presenting the one conductivity type, an optical absorption layer 13, a window layer 14 presenting an opposite conductivity type semiconductor, and a conduct layer 15 presenting the opposite conductivity type semiconductor in order on a substrate 10. The photodetector has p-n junction having a p-side electrode 17a on a light shielding film 16 and the layer 14, and an n-side electrode 17b on the rear surface of the substrate 10. In the semiconductor photodetector, the joint area of the interfaces of the layer 13 and the layer 15 is larger than that of the layer 13 and the layer 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element, and more particularly to a semiconductor light receiving element capable of using optical fiber communication.

[0002]

2. Description of the Related Art A conventional semiconductor light receiving element will be described with reference to FIGS. FIG. 3 is a perspective view of a GaAs mesa-shaped semiconductor light receiving element, and FIG. 4 is a sectional view.

An n-type GaAs buffer layer 21, an n-type AlGaAs layer 22, and an n ⁻ -type semi-insulating GaAs light absorption layer 2 on an n-type GaAs substrate 20.
3, the p ⁺ type AlGaAs window layer 24 and the p ⁺ type GaAs contact layer 25 are sequentially formed, the p side electrode 27a is provided on the surface of the p type GaAs contact layer 25, and the n side electrode is provided on the back surface of the GaAs substrate 21. 27b is provided,
Further, it has a structure in which a light shielding film 26 is provided on the light receiving surface.

In such a GaAs mesa-shaped semiconductor light receiving element, the GaAs buffer layer 21 contains n-type impurities of 1 × 10 ¹⁷ to.
It is added at a relatively high concentration of about 10 ¹⁹ atoms / cm ³ .

The AlGaAs layer 22 contains 1 × 10 ¹⁷ to 10 ^{19 of} n-type impurities.
It is added at a relatively high concentration of about atoms / cm ³ . GaA
Although the light absorption layer 23 is non-doped and does not contain impurities, it is actually an n ⁻ type with a low concentration of about 5 × 10 ¹⁵ atoms / cm ³ . AlGaAs window layer 24 is 1 × 10 ¹⁷ to 10 ¹⁸ ato
It has a p ⁺ type of about ms / cm ³ . Contact layer 25 is 1 × 1
It is a p ⁺ type with about 0 ¹⁷ to 10 ¹⁸ atoms / cm ³ .

Here, a reverse bias voltage is applied from the p-side electrode 27a and the n-type electrode 27b to deplete the light absorption layer 23. When the incident light 29 enters in such a state, the carriers excited in the light absorption layer 23 are accelerated by the high electric field applied to the light absorption layer 23, and the n-type GaAs buffer layer 21 or p ⁺ Type AlGaAs window layer 24 to achieve a high speed response.

In order to further improve the light receiving efficiency of the semiconductor light receiving element having the above structure, a technique having a mesa shape type has been proposed (see Japanese Patent Laid-Open No. 7-153993).

In this technique, a relatively large amount of light can be extracted from the light emitted from the active layer by using the reflected light from the side surface of the mesa.

However, according to the GaAs-based mesa-shaped semiconductor light receiving element having the above-described structure as shown in FIGS. 3 and 4, P
The ends of the N-junction 28 and the light absorption layer 23 are exposed on the side surface of the mesa, and the incident light 29 leaking from the light receiving surface enters from the side surface of the element, carriers are generated in the lower portion of the light receiving area, and the light receiving area is formed. Since the traveling distance of the carrier is different between the carrier generated in and the carrier generated in the lower part of the light receiving area,
When the carrier travel times are different and this difference is detected as a signal, it appears as a tail state in the falling waveform, and the response speed of the element is reduced. Further, the generated carriers cause a surface leak current on the side surface of the mesa to increase the dark current.

In order to solve such a problem, after forming the light-shielding film 26, an inert impurity such as O ₂ ion implantation is introduced to make the mesa-shaped side surface a semi-insulating material between the mesa-shaped side surface and the insulating film. Method to reduce the dark current (Japanese Patent Laid-Open No. 2-15680) or a method to reduce the dark current by providing a multi-layer structure of a low-concentration layer and a high-concentration layer of the same conductivity type as the substrate on the side surface of the mesa. 8-162663) is proposed.

[0011]

However, in these methods, since the ion implantation, the film forming process after forming the mesa shape, and the like are performed, the manufacturing process is complicated.

Further, according to the GaAs mesa shape type having the above-mentioned structure, as compared with the area of the AlGaAs window layer 24 which receives the incident light 29,
The area of the PN junction becomes larger, the capacitance of the light receiving element increases, and the cutoff frequency showing the response of the element becomes smaller, resulting in a problem in high-speed operation of the element.

Therefore, the object of the present invention has been completed in view of the above, and an object thereof is to form a side surface having an inverted mesa shape so that a PN is formed on the mesa shape side surface without complicating the manufacturing process. It is an object of the present invention to provide a semiconductor light receiving element in which the dark current caused by the exposure of the end portion of the junction and the light absorption layer is reduced, and thereby the reduction of the response speed is prevented.

Another object of the present invention is to efficiently collect incident light incident on the end portion of the device, reduce the capacitance of the device by reducing the area of the PN junction, and achieve a high-speed semiconductor light receiving device. To provide.

[0015]

A semiconductor light receiving element of the present invention has a PN junction formed by sequentially forming a one-conductivity-type semiconductor layer, a light absorption layer, and a reverse-conductivity-type semiconductor layer on a substrate. In the above, the junction area at the interface between the light absorption layer and the opposite conductivity type semiconductor layer is made larger than the junction area at the interface between the light absorption layer and the one conductivity type semiconductor layer.

Another semiconductor light receiving element of the present invention is characterized in that each of the end faces of the opposite conductivity type semiconductor layer, the light absorption layer and the one conductivity type semiconductor layer has an inverted mesa shape.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to FIGS. FIG. 1 is a perspective view showing an embodiment of a semiconductor light receiving element of the present invention, and FIG. 2 is a schematic sectional view. This semiconductor light receiving element is exemplified by a GaAs pin photodiode.

In the semiconductor light receiving element of the present invention, 10 is a semiconductor substrate of one conductivity type (hereinafter referred to as substrate), 11
Is a buffer layer of one conductivity type, 12 is a semiconductor layer of one conductivity type, 13 is a light absorption layer, 14 is a window layer of the opposite conductivity type semiconductor, and 15 is a contact layer of the opposite conductivity type semiconductor.

Further, a light-shielding film 16 is provided on the side surface and the surface of the device, and the p-side electrode 17a and the substrate 10 are provided under the substrate 10 and on the window layer 14.
An n-side electrode 17b is provided on the back surface of the.

[0020] If the substrate 10 is a semiconductor substrate, for example made of one conductivity type impurity contained about ^{1 × 10 17 ~10 1 9 atoms} / cm 3, silicon (Si), gallium arsenide (GaAs), such as A single crystal semiconductor substrate is used.

The single crystal semiconductor substrate is preferably a substrate in which the (100) plane is off by 2 to 7 ° in the <011> direction.

The buffer layer 11, which is a semiconductor layer of one conductivity type, is made of gallium arsenide (GaAs) and contains impurities of one conductivity type (Si or the like).
Of about 1 × 10 ¹⁷ to 10 ¹⁹ atoms / cm ³ and 2 to 10
It is formed to have a thickness of about 3 μm, thereby preventing or reducing misfit dislocations due to lattice mismatch between the substrate 10 and the semiconductor layer above it.

The one-conductivity-type semiconductor layer 12 is formed of aluminum gallium arsenide (Al _x Ga _1-x As), and contains one-conductivity-type impurity (Si or the like) in a concentration of about 1 × 10 ¹⁷ to 10 ¹⁹ atoms / cm ³ . Then, it is formed to a thickness of about 0.2 to 2 μm.
The Al composition of the layer 12 is preferably x of 0.1 or more, whereby a discontinuity is formed in the energy band gap, and the p-side electrode 1 is generated in the light absorption layer 13.
The holes traveling to 7a are prevented from being diffused into one conductivity type semiconductor layer 12.

The light absorption layer 13 is made of gallium arsenide (GaAs) and is non-doped with no impurities. However, in reality, it contains one conductivity type impurity (S or the like) at about 5 × 10 ¹⁵ atoms / cm ^3. And has a thickness of about 2 to 3 μm.

The window layer 14, which is a semiconductor layer having a reverse conductivity type, is formed of aluminum gallium arsenide (Al _y Ga _{1- y} As),
Zinc (Zn) opposite conductivity type semiconductor impurity ¹ × 10 1 ⁷ ~10 ¹⁹ atoms of
It contains about atoms / cm ^{3 and} has a thickness of about 0.1 to 0.2 μm. Here, as the Al composition, when y is 0.1 or more, it is desirable in that discontinuity is formed in the energy band gap as described above. Further, the smaller the Al composition of the semiconductor layer 12 is, the more suitable it will be in etching to be described later (y <x). ) Or the like having a reverse conductivity type semiconductor impurity of about 1 × 10 ¹⁹ to 10 ²⁰ atoms / cm ^{3 and} a thickness of about 0.01 to 0.3 μm.

The light-shielding film 16 is made of silicon nitride (SiNx) or silicon oxide.
It is made of (SiO ₂ ), synthetic resin, etc. and has a thickness of about 3000 Å.

The p-side electrode 17a and the n-side electrode 17b are made of gold / gold / germanium (Au / AuGe) and have a thickness of about 1 μm.

Thus, according to the light-receiving element having the above structure, since the end surfaces of the reverse-conductivity-type semiconductor layer 14 and the light-absorbing layer 13 have the inverted mesa-shaped side surfaces inclined inward, the incident light 19 leaking from the light-receiving surface is prevented. , Incident on the semiconductor layer 12 exhibiting one conductivity type,
Carriers are not generated in the lower part of the light receiving region, and therefore, due to the difference in carrier transit time, the signal does not appear as a tail state in the falling waveform and the response speed of the element is not reduced. In addition, the generated carriers cause a surface leak current on the side surface of the mesa and prevent the dark current from increasing.

Incident light 19 incident on the end of the element propagates inside the element and exits at an interface having a different refractive index.
When the reverse mesa shape becomes stronger, the angle of incidence on the reverse mesa side surface becomes larger, and the reflectance at the reverse mesa side surface increases, which causes the reflected light to be condensed at the center of the element and absorbed by the light absorption layer 13. The number of photons generated increases, the number of carriers generated increases, and the light receiving sensitivity improves. Further, since it has an inverted mesa shape, it is possible to reduce the area of the PN junction 18 with respect to a planar shape or mesa shape element having the same light receiving area.
The capacitance of the element can be reduced, and as a result, the cutoff frequency showing the responsiveness of the element can be increased.

(Manufacturing Method of Semiconductor Light-Receiving Element of the Present Invention) Next, a method of manufacturing the semiconductor light-receiving element of the present invention by the MOCVD method will be described below with reference to a GaAs semiconductor light-receiving element.

The GaAs substrate 10 of one conductivity type is heated in a hydrogen (H ₂ ) and arsine gas (AsH ₃ ) atmosphere to 600 ° C. to 800 ° C.
Remove oxide on 10 surfaces.

Then, the substrate temperature is set to 500 ° C. to 800 ° C., trimethylgallium (hereinafter abbreviated as TMG), arsine gas (AsH ₃ ) and silane gas (SiH ₄ ) are supplied as dopant gases, and the Si concentration is 1.0 × 10 ¹⁷ A GaAs buffer layer 11 of about 10 ¹⁹ atom / cm ³ is formed with a thickness of 2 to 4 μm.

Next, TMG, trimethylaluminum (hereinafter abbreviated as TMA), arsine gas (AsH ₃ ) and silane gas (SiH ₄ ) were supplied as dopant gases, and the Si concentration was 1.
The semiconductor layer 12 exhibiting ^{0 × 10 1 7 ~10 19 atom} / cm 3 one conductivity type semiconductor is formed to a thickness of 0.2 to 2.0 [mu] m.

On top of that, TMG and arsine gas (AsH ₃ ) are used as source gases, and a GaAs light absorption layer 13 having a semi-insulating property is formed.
Is formed with a thickness of 2.0 to 3.0 mm.

Then, TMG, TMA, arsine gas (A
sH ₃ ), and dimethylzinc (hereinafter abbreviated as DMZ) as a dopant gas, and the Zn concentration is 1.0 × 10 ¹⁷ to 10 ¹⁹ atom / cm 2.
^A window layer 14 having a reverse conductivity type semiconductor made of aluminum gallium arsenide (AlGaAs) ³ is formed to a thickness of 0.1 to 2.0 μm.

After that, the window layer 14 which exhibits an opposite conductivity type semiconductor made of aluminum gallium arsenide (AlGaAs) using dimethylzinc (hereinafter abbreviated as DMZ) as a dopant gas.
To have a thickness of 0.1 to 0.2 μm.

The crystal after such growth forms an inverted mesa structure by using a sulfuric acid-hydrogen peroxide type etching solution.
When this etching solution is used, aluminum gallium arsenide has a faster etching rate than gallium arsenide, and the higher the aluminum composition ratio among the aluminum gallium arsenide, the higher the etching rate.

The aluminum gallium arsenide _{(Al x Ga 1-x As} ) one conductivity type semiconductor layer 12 made of, in between the aluminum gallium arsenide _{(Al y Ga 1-y As} ) opposite conductivity type semiconductor layer 14 made of , Y <x, the layer forming the semiconductor layer 12 has the fastest etching rate and the thinnest cross-sectional shape, and the one conductivity type semiconductor layer 12, the light absorption layer 13, and the opposite conductivity type semiconductor layer 14 are Inverted mesa The shape becomes an inverted mesa.

Subsequently, the gallium arsenide contact layer 15 is etched using a sulfuric acid-hydrogen peroxide type etching solution to form a light receiving region.

After that, silane gas (Si
The light shielding film 18 made of silicon nitride (SiNx) is formed using H ₄ ) and ammonia (NH ₄ ).

Thereafter, the p-side electrode 17a is formed of gold / germanium (AuGe) or the like by using the vapor deposition method or the sputtering method. Similarly, the n-side electrode 17b is formed on the back surface of the substrate.

[0042]

As described above, in the light receiving element according to the present invention, a PN junction is formed by sequentially forming on the substrate a semiconductor layer having one conductivity type, a light absorption layer, and a semiconductor layer having an opposite conductivity type. In the semiconductor light receiving element which has, the bonding area at the interface between the light absorption layer and the opposite conductivity type semiconductor layer is made larger than the bonding area at the interface between the light absorption layer and the one conductivity type semiconductor layer. Since the end faces of the light absorption layer and the semiconductor layer of one conductivity type have the inverted mesa-shaped side faces inclined inward, the manufacturing process is not complicated, and the PN junction and the light It was possible to provide a semiconductor light receiving element in which the dark current caused by the exposed end of the absorption layer was reduced and the response speed was prevented from decreasing.

Further, in the semiconductor light receiving element of the present invention, by forming the side surface having the inverted mesa shape, the incident light incident on the end portion of the element can be efficiently collected and the area of the PN junction is reduced. As a result, the capacitance of the device was reduced and a high-speed semiconductor light receiving device could be provided.

[Brief description of drawings]

FIG. 1 is a perspective view of a semiconductor light receiving element of the present invention.

FIG. 2 is a sectional view of a semiconductor light receiving element of the present invention.

FIG. 3 is a perspective view of a conventional semiconductor light receiving element.

FIG. 4 is a sectional view of a conventional semiconductor light receiving element.

[Explanation of symbols]

10 ... Semiconductor substrate 11 ... Buffer layer exhibiting one conductivity type 12 ... Semiconductor layer exhibiting one conductivity type 13 ... Light absorbing layer 14 ... Window layer exhibiting reverse conductivity type semiconductor 15 ... Contact layer exhibiting reverse conductivity type semiconductor 16 ... Shading film 17a ... p-side electrode 17b ... n side electrode

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Claims (2)

[Claims] 1. A semiconductor light-receiving element having a PN junction, in which a semiconductor layer of one conductivity type, a light absorption layer, and a semiconductor layer of opposite conductivity type are sequentially formed on a substrate. A semiconductor light-receiving element characterized in that the junction area at the interface is made larger than the junction area at the interface between the light absorption layer and the one-conductivity-type semiconductor layer. 2. The semiconductor light receiving element according to claim 1, wherein each of the end faces of the opposite conductivity type semiconductor layer, the light absorption layer and the one conductivity type semiconductor layer has an inverted mesa shape.